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• Energy is the ability to do work.
• As such, energy is important to all living things in order to maintain life functions from the smallest part of a cell to the organism as a whole.
Humans also use energy to modify their environment and perform work.
• Energy is measured by the amount of work it is able to do. The units for measuring energy are
Joules (J).
• One Joule is a very small amount of energy, but 1000 Joules is roughly the heat energy produced by burning a blue tip kitchen match.
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• The energy sources that we use every day are divided into two groups:
– Renewable – an energy source that we can use over and over again, and can be replaced naturally in a short period of time.
– Non-renewable – an energy source that we are using up and cannot recreate in a short period of time.
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• Work can be done at different rates, sometimes slow, sometimes fast. Since work involves the transformation of energy, the faster the work is done, the quicker energy must be transformed.
• Power is the term used for the measure of how fast work can be done. Or in other terms, power is defined as the rate at which work is done.
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• In mathematical terms power equals work done divided by time required, so the units of power would be Joules per unit time, most commonly
Joules per second, or watts:
Power
=
Work Done
Time Required
• Power is an important concept because it ties the dimension of time into the energy picture.
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• Almost all mechanical and electrical equipment have nameplate ratings in terms of the maximum power that they can supply, not the energy they can supply.
• As we will see later, almost all mechanical devices like motors are rated in terms of their maximum power output , while almost all purely electrical devices are rated in terms of their maximum power input .
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• Energy and power are often confused with each other.
• A useful analogy can be found in our car where we have both the speedometer that tells us how fast we are going in kmph, and we also have an odometer which tells us how far we’ve gone in km.
KMPH
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– The odometer is like an energy meter that tells us the total amount of energy in Joules that we’ve used.
KMPH
– The speedometer is like a power meter that tells us the rate at which we have used that amount of energy in
Joules per second, or watts.
• With our car, the quantities of interest are km and kmph. With our electrical and mechanical equipment, the quantities of interest are Joules and
Joules per second, or watts.
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• When dealing with electricity, power is defined in the same way.
• Electrical devices provide resistance which describes the amount of work that needs to be done for a specific task.
– A certain amount of work must be done to move electrons through the resistance.
– More resistance means more work must be done to move electrons through the resistance and allow the device to operate.
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• The rate which that work is accomplished is related to the power applied. More electrical power means energy is being converted at a faster rate.
• This electrical energy is supplied by the source of the electrical current like a battery or electrical generator.
1 watt = 1 Joule/second
• Electrical power is measured in units called watts, which are related to the number of Joules of energy expended per second.
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• This means the energy can be expended at different rates depending on how fast the work needs to be done.
• Some devices use more power to accomplish a task that others do with much less power.
• For example light bulbs come in different sizes – meaning different wattages. Some light bulbs are rated 60 watts while others are rated 100 watts. The 100 watt bulb will give off more light than the 60 watt bulb but if you only need the amount of light from the
60 watt light bulb, you are using more power than necessary.
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• The watt (W) is a physical unit which is named for James Watt, the inventor of the steam engine. Since the unit refers to a person’s name, we abbreviate it with a capital W.
• The basic unit of electrical energy is the watt-hour, or
Wh.
1 Wh = 3600 Joules
1 kWh = 1000 Wh = 3600000 Joules = 3.6 MJ
1 MWh = 1000 kWh
1 GWh = 1000 MWh
1 kW = 1000 W
1 MW = 1000 kW
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15

16

degree s Celsiu s
minut es
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• The basic unit of energy is the Joule (J)
• One thousand Joules is about equal to the heat produced by burning an ordinary blue-tip, kitchen match.
• One Joule is not a very large amount of energy, so you will often see one of two common multipliers of Joules; the kJ, or one thousand Joules; or the MJ, which is 1000 kJ, or one million Joules. For even larger amounts of energy, the GJ = 1000 MJ.
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• One J = 1 J.
• One thousand J = 1000 J = 10 3 J = 1 kJ
• One million J= 1,000,000 J = 10 6 J = 1 MJ
• One billion J = 1,000,000,000 = 10 9 J = 1 GJ
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1 kWh ………………………………………….. 3.6 MJ
1 m 3 LPG……….…………………………….25.56 GJ
1 kg #2 fuel oil …………………………….… 43.3 MJ
1 m 3 natural gas………………………….……. 37 MJ
1 m 3 #2 fuel oil ………………………………39.85 GJ
1 litre LPG gas ……………………………... 7.1 kWh
1 kg LPG gas………………………………12.68 kWh
1 litre #2 fuel oil……………………………11.07 kWh
1 kg #2 fuel oil……………………………..12.03 kWh
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• Since we have several different basic energy units and many different energy unit multipliers, energy managers must often convert from one set of energy units to another. There is a very systematic approach that can be applied to basic conversions, and also to more complex conversions and calculations.
• The principle of this unit conversion method is simply to carry out algebraically correct multiplications and divisions using correct units at each step, starting with the given piece of information and transforming it into the desired units using one or more conversion factors.
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• For example, if we want to find the number
(X) of Joules in 1000 cubic metres of natural gas, we can use this method as follows:
X GJ of gas =
1000 m 3
=
1000 m 3 m 3
37 , 000 kJ m 3
37 , 000 kJ
From Table C-20
= 1000 37,000 kJ
= 37 10 9 J
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• In the above calculation, cubic metres in the numerator and cubic metres in the denominator cancel out, and the remaining unit on the right side of the equation is J.
• Our goal was to end up with J as our desired unit on the right, and we made our unit conversions on the right side until we had the same unit as on the left side.
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• If we ever perform one of these basic unit conversion calculations, and find that we have different units on the left and the right – we do not have the correct answer in terms of the desired units.
• This method is given the colloquial name Railroad Track Method, because the vertical separation lines remind us of railroad tracks.
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Find the number (X) of kWh in 1000 cubic metres of natural gas.
X kWh of gas =
1000 m 3
=
1000 m 3 m 3
37 , 000 m 3 kJ 1 kWh
3600
37 , 000 kJ kJ
1 kWh
3600 kJ
From Table C-20
= 1000 37,000 kWh/3600
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How many J are in 10 kWh?
Solution
X J = 10 kWh 3.6 MJ
kWh
= 36 MJ
In this example, the two kWh units cancel out, leaving the remaining unit on the right side as J.
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How many kWh are in 2500 mJ?
Solution:
X kWh =
2500
= 694 .
44
MJ 3 .
6 kWh
MJ kWh
In this example, the two MJ units cancel out, leaving the remaining unit on the right side as kWh.
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• A tank is filled with 100 litres of Number 2 fuel oil. How many GJ of energy is contained in the tank of oil?
Solution
• From Table C-20, there are 39 MJ per litre of oil.
X GJ =
100 L 39
1
MJ
L
1 GJ
1000 MJ
= 3.9 GJ
• In this example, the two litre units cancel out, and the two MJ units cancel out, leaving the remaining unit on the right side as GJ, our desired unit.
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• A tank is filled with 100 litres of Number 2 fuel oil. How many kWh of energy is contained in the tank of oil?
Solution
• From Table C-20, there are 39 MJ per litre of oil.
X kWh =
100 L 39
1
MJ
L
1
3 .
kWh
6 MJ
= 1083.3 kWh
• In this example, the two litre units cancel out, and the two MJ units cancel out, leaving the remaining unit on the right side as kWh, our desired unit.
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• Building energy benchmarking is the comparison of whole-building energy use relative to a set of similar buildings.
• It provides a useful starting point for individual energy audits and for targeting buildings for energy-saving measures in multiple-site audits.
• Benchmarking is of interest and practical use to a number of groups.
– Energy service companies and performance contractors communicate energy savings potential with “typical” and “best-practice” benchmarks.
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• Control companies and utilities can provide direct tracking of energy use and combine data from multiple buildings for benchmarking.
• Benchmarking is also useful in the design stage of a new building or retrofit to determine if a design is relatively efficient.
• Energy managers and building owners have an ongoing interest in comparing energy performance to others.
• Large corporations, schools, and government agencies with numerous facilities also use benchmarking methods to compare their buildings to each other.
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• Benchmarking Audits are associated with the idea that after the energy bill data is collected and processed, some facility information will be collected on a walkthrough, and the data will be run through some benchmark to determine if there is a potential for significant improvement in energy efficiency and reduction in energy operating cost.
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• Energy Use Index - MJ/m 2 /year, kWh/m 2 /year
– Total, Electric, Gas, Oil
• Energy Cost Index - $/m 2 /year
– Total, Electric, Gas, Oil
• Productivity Index
– kJ/kg, kJ/person, kJ/student, kJ/tonne, kJ/item
– kWh/kg, kWh/person/ kWh/tonne, kWh/item
– L H
2
O/kg, or /student, or /item (also sewer)
• System performances
– kWe/kW cooling, LPS/kW air, kWh/L pumping
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• Basic energy accounting deals with the following ideas:
• Recognizing different energy and fuel types
– Electricity, gas, light oil, steam, chilled water
• Understanding energy related units
– kWh, kJ, MJ, kW, kJ/h, L or kg of oil, m 3 of gas
• Performing conversions to different energy related units
– For example, 1 kWh = 3600 kJ = 3.6 MJ
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• The facility Energy Use Index (EUI) is a statement of the number of MJs (or kWh) of energy used annually per square metre of conditioned space (heated or cooled, or both).
It is a basic measure of the facility’s energy performance – the lower, the better.
• To compute a facility’s EUI –
– Identify all the energy used in the facility
– Add up all the MJs (or kWh) of energy
– Find the total square metres of conditioned space
– Divide the total MJ (or kWh) used per year by the square metres of space.
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2
MJ gas
=
100 yr
GJ 1000
GJ
MJ
= 100 , 000 MJ / yr
MJ elect
=
150 , 000 yr kWh 3 .
6 MJ kWh
= 540 , 000 MJ / yr
EUI =
( 100 , 000 +
1 , 000
540 , 000 ) m 2 yr
MJ
= 640 MJ / m 2 • yr
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2
EUI =
640 m 2 •
MJ yr
1
3 .
kWh
6 MJ
= 177 .
8 kWh / m 2 • yr
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1999 CBECS EUI Data - USA kWh/m 2 /yr
All Bldgs
Education 208
Food Sales
Health Care
236
561
490
Retail Stores 200
Vacant 44.5
Food Service 669
Lodging
Office
278
251
Assembly 228 Safety 242
Churches 88.9 Service 346
Warehouse 122 Other 400
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Energy Use Index for Commercial Buildings kWh/sq metre/yr
700
600
500
400
300
200
100
0
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